Stability of large room airflow structures in a ventilated room

This paper presents a new set of experimental data for different kinds of room airflows in a ventilated room. The data are used to examine Archimedes number effects on the behaviour of large-scale flow structures and their stability versus time. All experiments are performed in a simplified room geometry, representing a small meeting room, a train or an airplane cabin. The supply air is introduced at the ceiling and the exhaust air leaves the room at the bottom zone. The heating power is realised by four controllable heat sources in the lower part of the model room. The experimental investigations apply different supply air set-ups as well as changing supply air velocities and a variation of the heating power. The data of the experiments indicate that the room geometry-based Ar number can be used to distinguish between unstable to stable room airflow structures. Low velocities and high thermal loads cause time depended, unstable room airflows. Neither the forced nor the free convection dominates the flow structure. By increasing the inlet velocity, the airflow structure gets more stable. Large eddies occur between the heat sources and the ceiling of the model room. This experimental investigation showed that it is possible to determine an Ar number for the room geometry under investigation, in the region where a transition takes place from instable to stable airflow. The value of this critical Ar number has been extracted from a qualitative velocity profile analysis.